This application claims the priority of German Application No. 196 30 871.2, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a process and a system for stopping a vehicle which utilizes a device for the braking intervention via an external power.
Because of the stiff converter, the high internal-combustion engine torque and the high, driving-performance-oriented starting ratio, particularly in the case of high-performance, top-of-the-line vehicles having an automatic transmission, the vehicles have a strong tendency to creep when in gear in a stopped condition. In addition, a socalled "brake creaking" may occur because of a constant slip stick (slipping) effect, which is the transition from the static friction to the sliding friction and vice versa. For solving this problem, German Patent Document DE 43 32 459 suggests aiding the braking effect of the vehicle service brake (operator controlled foot brake pedal) via a separate device. In this case, it is a disadvantage that the vehicle operator can leave the vehicle while the engine is running and the gear selector lever is engaged.
The separate device for aiding the braking effect increases the costs in a disadvantageous manner. In addition, in the case of an excessive creeping action of the vehicle, the vehicle operator must apply a braking force which is dimensioned proportionally with respect to this creeping action even when there is additional assistance.
It is an object of the present invention to provide an improved and lower-cost process and system for stopping a vehicle.
This and other objects have been achieved according to the present invention by providing a process for stopping a vehicle having an operator-controlled primary brake circuit and a secondary brake circuit, comprising the steps of: sensing a velocity of the vehicle; sensing an operator-applied braking input to the primary brake circuit; applying an additional braking pressure via the secondary brake circuit when the velocity falls below a defined limit value and the operator-applied braking input is sensed; and terminating the applying step when the operator-applied braking input is no longer sensed.
This and other objects have also been achieved according to the present invention by providing a system for stopping a vehicle, comprising: an operator-controlled primary brake circuit; a secondary brake circuit controlled by a control unit; a velocity sensor which senses a velocity of the vehicle; a braking input sensor which senses an operator-applied braking input to the primary brake circuit; wherein the control unit applies an additional braking pressure via the secondary brake circuit when the velocity sensor senses a velocity below a defined limit value and the braking input sensor senses the operator-applied braking input, and wherein the control unit terminates applying the additional braking pressure when the braking input sensor no longer senses the operator-applied braking input.
Many of today's vehicles have devices for exercising a braking intervention by means of an external power or a secondary brake circuit. Such devices are, for example, a dynamic stability control or traction control system, an anti-slip control or the so-called anti-lock braking system. By means of the valves and pumps provided in these systems, it is possible to separate the brakes assigned to the individual wheels from the primary brake circuit and connect them to a secondary circuit which is normally acted upon by means of a pump by braking pressure. According to the operation of the pump and the corresponding control measures, more or less braking pressure can be supplied to the brake cylinders of the corresponding wheels. As a result of the utilization of the already existing devices, it is no longer necessary to take separate measures, as known, for example, from German Patent Document DE 43 32 459. Also, the insufficient metering capacity of the vehicle user must no longer be used but a braking pressure can be automatically determined which is adapted to the respective conditions.
In the process according to the invention, at a certain rate or input of the braking intervention, the brake pressure is first "shut in", i.e., maintained. The process according to the invention is carried out only below a certain vehicle limit speed and at an active braking intervention by the vehicle operator which exceeds a predetermined first rate. As the rate or input for the active braking intervention, the operation of the brake light switch or the recognition of a brake pressure which exceeds a predetermined limit value, for example, may be used, or a sensed position of the foot brake pedal. During the external braking operation, the input exercised by the vehicle operator, e.g., the input brake pressure, is constantly compared with given input values, e.g., given brake pressure values. As soon as the brake pressure falls below these given brake pressure values, the braking intervention is terminated. For example, the conclusion can be drawn from sensing a brake pressure which is lower than a given limit value that the driver does not want to stop at that time.
As soon as the braking intervention takes place via an external power or secondary brake circuit, brake pressure is no longer applied to the individual wheels via the primary brake circuit controlled directly by the vehicle operator because the primary brake circuit (master brake cylinder) is uncoupled from the wheels via valves.
Other vehicle conditions, such as the engaged gear position (for example, R, D, 3, 2, 1) or the operation of the engine may also be queried and can be included in the decision of whether to initiate an external braking operation via the secondary brake circuit.
A value corresponding to the actual brake pressure is preferably stored at the start of the external braking operation. As a result of the comparison of a desired brake pressure value corresponding, for example, to a position of the foot brake pedal, with the stored brake pressure value, a conclusion can be drawn concerning the driver's intention, for example, with respect to intending to carry out parking maneuvers or starting.
According to certain preferred embodiments of the present invention, at the start of the external braking operation via the secondary brake circuit, the brake pressure is increased by an offset amount, specifically preferably according to a fixed pressure buildup function. A slow increase of the brake pressure ensures that the vehicle will stop smoothly if it has not yet stopped completely, which can be required particularly in the case of the passive rotational speed sensors. This gives the vehicle operator the impression of a slowly coasting-out vehicle.
At the conclusion of the external braking intervention, the brake pressure should preferably be reduced according to a fixed course. As a result, a jerky starting is avoided.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.